Rotating media storage devices are an integral part of computers and other devices with needs for large amounts of reliable memory. Rotating media storage devices are inexpensive, relatively easy to manufacture, forgiving where manufacturing flaws are present, and capable of storing large amounts of information in relatively small spaces.
A typical rotating media storage device uses a rotatable storage medium with a head disk assembly and electronics to control operation of the head disk assembly. The head disk assembly can include one or more disks. In a magnetic disk drive, a disk includes a recording surface to receive and store user information. The recording surface can be constructed of a substrate of metal, ceramic, glass or plastic with a thin magnetizable layer on either side of the substrate. Data is transferred to and from the recording surface via a head mounted on an arm of the actuator assembly. Heads can include one or more read and/or write elements, or read/write elements, for reading and/or writing data. Drives can include one or more heads for reading and/or writing. In magnetic disk drives, heads can include a thin film inductive write element and a magneto-resistive (MR) read element.
An actuator, such as a Voice Coil Motor actuator, is used to position the head assembly over the correct track on a disk by rotating the arm. Typically, when the drive needs to move the head to a desired track, if the head is relatively far form that track, it starts out in a non-linear seek mode where the target velocity approximates a square root of the tracks to go (TTG). Once the head gets close to the target track, the drive typically switches over to a settle mode where the target velocity is a linear function of the tracks to go. Finally, once the head gets close enough to the target track for read/write operations, the drive then switches to a track-following mode. Typically, the same linear control law as in the settle mode is used, except with different parameters.